A crystalline epoxy resin generally has high heat resistance because of its rigid main chain skeleton and polyfunctionality, and is used in fields requiring heat resistant reliability, such as electric and electronic fields.
However, there are fields wherein a liquid composition must be used in molding, e.g., cast molding, depending on applications, and the crystalline epoxy resin is mainly used in applications using a solid material, e.g., transfer molding.
Furthermore, the conventional epoxy resin to be used for the liquid molding such as cast molding is a liquid epoxy resin, which cannot sufficiently meet a demand for improvement in cured product properties such as heat resistance, more severely required recently in fields of adhesion, cast molding, sealing, molding, laminating, and so on. Therefore, there are increasing demands for liquefying a crystalline polyfunctional epoxy resin which provides cured product properties including high heat resistance. On the other hand, there are also increasing demands for stability of a cured product in short-wavelength regions such as white LED and blue LED.
Patent Document 1 describes that a liquid modified epoxy resin is obtained by reacting a crystalline epoxy resin with a compound having at least two phenolic hydroxyl and/or carboxyl groups in one molecule and a compound having one phenolic hydroxyl group and/or carboxyl group in one molecule.
Patent Document 2 discloses a process for producing a liquid epoxy resin composition with fluidity at room temperature, wherein a mixture containing a crystalline epoxy resin and a liquid acid anhydride curing agent is melted and mixed at a temperature higher than the melting point of the epoxy resin for at least 10 minutes to cause reaction of the mixture, thereby obtaining a noncrystalline epoxy resin.
Patent Document 3 discloses a tris-(2,3-epoxypropyl)-isocyanurate composition which is liquid at room temperature, and which comprises 100 parts by weight of a low-melting point stereoisomer of tris-(2,3-epoxypropyl-isocyanurate with a melting point of from 98 to 107° C. and an epoxy value of at least 9.9, and such parts by weight of a carboxylic anhydride as a curing agent that a ratio thereof is 0.5 to 1.5 per epoxy group in the entire epoxy resin.
Patent Document 4 discloses a method for preventing crystallization, as a method for preventing solidification due to recrystallization of a liquid composition containing a trivalent epoxy compound with a triazine skeleton and an acid anhydride curing agent, characterized in that a water content in the composition is adjusted to at most 0.5% by weight.
Patent Document 1: JP-A-7-62060 (scope of claims)
Patent Document 2: JP-B-6-68014 (scope of claims)
Patent Document 3: JP-A-4-264123 (scope of claims)
Patent Document 4: JP-A-4-81420 (scope of claims)